Method for controlling the heating of a metal immersed in a plating solution

ABSTRACT

IN THE PLATING OF A CONTINUOUSLY MOVING METAL SUBSTRATE IMMERSED IN A PLATING SOLUTION PROVIDED WITH A MEANS FOR CONTINUOUSLY HEATING THE SUBSTRATE, THE HEAT INPUT TO THE SUBSTRATE IS CYCLED BY MEANS THEREFOR TO GIVE A SERIES OF HEAT INPUTS AND QUENCHING STEPS SO AS TO MANIPULATE THE TEMPERATURE OF THE SUBSTRATE WITHIN A TEMPERATURE RANGE SUITABLE FOR PLATING TO THEREBY ACHIEVE A QUALITY COATING OF A DESIRED THICKNESS.

United States Patent Stovall Mar. 28, 1972 [54] METHOD FOR CONTROLLING THE 2,944,874 7/1960 Irvine, .Ir ..117/113 x HEATING OF A METAL IMMERSED [N 2,955,959 10/1960 Du Rose A PLATIN s UTION 3,190,771 6/1964 McLean et al..

C 0L 3,513,014 5/1970 lnove [72] Inventor: William B. Stovall, Seabrook, Tex. 3,554,782 1/1971 Nieberlein [73] Assigneez Continental 0 company, Ponca City, 3,572,286 3/1971 Forney ..117/93.2 X

Okla' Primary Examiner-Alfred L. Leavitt [22] Filed: Sept. 3, 1970 Assistant Examiner-J. R. Batten, Jr.

Attorney-Joseph C. Kotarski, Henry H. Huth, Robert B. [21] Appl' 69222 Coleman, Jr., Ronnie D. Wilson and Carroll Palmer [52] 0.5. CI ..117/93, ll7/93.2, 117/113, [57] ABSTRACT 117/115, 117/128, 117/130R {51] lnt.Cl ..C23c 3/00 I t l n the plating of a continuously movmg metal substrate 1m- [58] Field ofSearch ..117/115,93,93.2, 128,113 mersed in a platingsolution provided with a means for [56] References Cited continuously heatlng the substrate, the heat 1nput to the substrate 1s cycled by means therefor to g1ve a series of n- STATES PATENTS heat inputs and quenching steps so as to manipulate the temperature of the substrate wlthin a temperature range 1,590,608 6/1926 Taylor ..117/93 UX i bl f l ti [0 thereby achieve a quality coating of 2,523,461 9/1950 Young et a1. ..117/113 X a desired thickness 2,698,810 1/1955 Stauffer ...117/128 X 2,834,692 5/1958 Tarna ..117/115 X 5Claims,2DrawingFigures P'ATENTEnuma m2 FIG. 2

INVENTOR.

WILL/AM B. STOVALL ATTORNEY METHOD FOR CONTROLLING THE HEATING OF A METAL IMMERSED IN A PLATING SOLUTION This invention relates to an improved method for plating elongated metal members, and more particularly, but not by way of limitation, to an. improved method for plating aluminum on wire.

Many techniques for plating elongated metal members, including plating aluminum on wire, have been proposed. In the majority of the prior art techniques, the wire is alternately heated and immersed in the plating solution, such as an aluminum alkyl solution, in a cyclic fashion until the desired thickness of coating is obtained. This cyclic type of technique requires an undue length of time and if the partially coated wire is not maintained in an inert atmosphere between the immersion steps, an oxide layer tends to form on the previously deposited aluminum which is detrimental to the completed coating.

Another technique used for plating a metal substrate such as a wire, involves continuously heating the wire submerged in and moving through a plating solution. Initially upon heating, the temperature of the wire will rise rapidly to the decomposition temperature of the plating solution. At this point, because of decomposition and vaporization effects, the wire is blanketed with a gas. This so-called gas envelope greatly reduces the rate of heat removal from the wire into the solution and with the heating of the wire continuing its temperature continues to rise to a point above a desired plating range, thereby causing detrimental effects to the coating being plated on the wire. In other words, good plating takes place in a temperature range with varying limits depending on the constituents employed. Above the suitable temperature range the plating is of poor quality and below the range no plating occurs. Since the temperature of the substrate being coated is a major factor in achieving a quality coating, it is desirable to keep the temperature of the substrate within the plating range.

It is an object of this invention to provide a method for plating an elongated metal member in a continuous fashion and in a minimum oftime.

Another object of this invention is to produce a coating on an elongated metal member with a single immersion of the member in a plating solution.

A further object of this invention is to control the heating of an elongated metal member during coating of the member to provide the desired thickness ofcoating.

A still further object of this invention is to control the heating of an elongated metal member while the member is submerged in the plating solution to achieve a coating of good quality.

Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings illustrating suitable apparatus to be used in the practice ofthe invention.

It has now been discovered that by controlling the power output of means for heating a metal substrate being plated by the decomposition of a plating solution while immersed therein with an external power supply so as to transmit defined pulses of heat input at defined intervals to the metal substrate, the temperature of the metal substrate is manipulated within a suitable range for achieving quality plating thereon. The cycling of heat inputs to the metal being coated enables one to control the heating and cooling cycles of the submerged metal, thereby obtaining optimum plating conditions.

In the practice of the present invention, the control of the heat inputs to the metal being plated consequently determines the heating and cooling cycles of the immersed metal. In producing a defined cycle of heating and cooling of the metal, more plating solution is allowed to contact the metal being plated than could otherwise be allowed by continuous heating of the metal. Upon heating the metal submerged in a plating bath to the decomposition temperature of the plating solution, a gas envelope is formed around the metal by the organics present in the solution (ethylene and hydrogen in the case ofa diethyl aluminum hydride solution) which do not permit the solution to contact the metal and therefore interfere with plating. By cycling the heat inputs to the metal at defined intervals, the metal is allowed to cool and lose the so-called gas envelope which consequently permits more plating solution to contact the metal to achieve more plating thereon. Further, by the above described cycling of heat inputs to the metal to be plated, conditions for the plating of a selected metal in a selected plating solution are easily manipulated to achieve optimum plating results.

FIG.'1 is a schematic illustration in the nature of a vertical sectional view through a suitable apparatus for practicing the method of the present invention.

Referring to the drawings in detail, and particularly FIG. 1, reference character 10 designates a bath of the plating solution, such as an aluminum alkyl liquid, which will be contained in a suitable vessel (not shown). The elongated metal member 12, such as a steel wire, to be coated is extended from a supply roll 14 downwardly into the bath l0 underneath an idler roller 16 and then extends along a straight path through the bath l0 underneath another idler roller 18 prior to being extended upwardly out of the bath to a takeup roll 20. The supply roll '14 and takeup roll 20 may be operated by any desired mechanism to move the wire 12 through the bath 10 at the desired speed, as is well known in the art.

An induction heating coil 22 is immersed in the bath l0 and surrounds the path of movement of the wire through a portion of the distance between the idler rollers 16 and 18 to form what may be considered a heating zone in the bath. The left hand end 24 of the coil 22, as viewed in the drawing, may be considered the entry end of the heating zone and the right hand end 26 may be considered the discharge end of the heating zone, since the wire 12 is moved from the left to the right as viewed in the drawing. The induction coil 22 is connected to a suitable adjustable power supply 50 by leads 52 and 54 for controlling the current supplied to the coil and thereby inductively heat the wire 12 to the desired plating temperature. An inert atmosphere, preferably nitrogen, is present above the plating solution.

FIG. 2 illustrates a suitable arrangement of an apparatus when the metal substrate is heated by resistance heating.

It is imperative to achieve the stated objectives of the method of the present invention that power supply 50 be of such a nature that it can be set to send pulses of power to the means for heating (induction coil 22 in FIG. 1) of a predetermined amplitude and be so constructed to control the frequency and duration of each pulse of power.

The adjustable power supply 50 for the purposes of this invention may be constructed of any conventional electrical timing and switching devices capable of performing the stated functions.

Because of the many variables involved in a plating process, for example the type of plating solution, the type of metal being plated, etc., the amplitude of a given pulse of power and its frequency and duration will vary depending on the desired result. Just for the sake of example, the power might be applied every second for two-tenths of a second or every three seconds for one-half of a second.

Further, the suitable temperature range for achieving quality plating will also vary depending on the type of metal being plated, and the plating solution being employed. Typically, a suitable plating range would be from about 350 C. to about 500 C.

It should be noted that the method of the present invention can be employed in any plating process which heats the metal substrate being plated by resistance heating, induction or other electrical means.

The invention has thus been described, I claim:

1. A method for controlling the temperature of a continuously moving elongated metal substrate being plated by the decomposition of a plating solution while immersed therein with an external power source connected to a means for heating said substrate in the plating solution to provide a plating of good quality, the method comprises:

transmitting defined pulses of power from said power source to said means of heating at defined intervals to manipulate the heat input of said means to said metal substrate; said pulses being so cycled to alternately raise the temperature of said plating solution to a temperature above the decomposition point of said solution and to allow for cooling of said substrate in said intervals by the effect of quenching by the plating solution to thereby control the temperature of said substrate to achieve a quality plating thereon.

The method of claim 1 wherein said means of heating is an electrical heater. 

2. The method of claim 1 wherein said means of heating is an electrical heater.
 3. The method of claim 2 wherein said metal substrate is a wire.
 4. The method of claim 2 wherein said defined pulses of power are of a pre-set amplitude lasting for a pre-set period of time and said defined interval is a pre-set period of time between the transmittance of said pulses of power.
 5. The method of claim 2 wherein said external power source is capable of being adjusted to supply various amplitudes of power lasting for varying periods of time at varying time intervals. 